Transformers are widely used in the wireless communication, such as chip-to-chip wireless communication, in which signals are transmitted from one chip to a neighboring chip wirelessly. One application of the chip-to-chip wireless communication is the signal transmission between a memory (for example, a dynamic random access memory (DRAM)) and a graphics processing unit (GPU). Due to the big number of transformers that may be used in the chip-to-chip wireless communication, the coupling-coefficients (k) of the transformers became a very important factor for reducing power consumption, for increasing communication distances, and for increasing signal-to-noise ratios.
Conventionally, to improve the k values of transformers that include two inductors formed on different chips, various approaches have been taken, which include reducing the thickness of chips so that the distances between the inductors may be reduced. This requires the chips to be ground to a very small thickness, and hence the process complexity in the handling of the respective wafers and chips is increased, and a higher cost may be involved. The improvement in the k values of the transformers may also be achieved by increasing areas of the transformers, and increasing magnetic flux density in the transformers. These methods, however, cause the chip area occupied by the transformers to be increased. For applications in which many transformers are involved, the increase in the chip area may be significant.